In a background art, a charged particle. beam apparatus of carrying out working, observation or the like by irradiating a charged particle beam of an ion beam, an electron beam or the like to a predetermined position has been used in various fields. As a charged particle beam apparatus, there is, for example, a scanning electron microscope (SEM) capable of irradiating an electron beam as a charged particle beam, or a focused ion beam apparatus (FIB) capable of irradiating a focused ion beam as a charged particle beam or the like. According to a scanning electron microscope, a state of a surface of the sample can be observed by detecting a secondary electron generated from the surface of the sample while scanning an electron beam on the surface of the sample. Further, according to the focused ion beam. apparatus, the surface of the sample can be observed by detecting a secondary electron similar to a scanning electron microscope, etching or deposition of a sample can be carried out by making an acceleration voltage high, and the focused ion beam apparatus is used for forming a sample of TEM (transmission electron microscope), correcting a photomask or the like. Further, in recent years, in a focused ion beam apparatus, attention is paid to a method of realizing a low damage working by using the focused ion beam apparatus in a low acceleration region of setting an acceleration voltage of a focused ion beam to about 100 V through 5000 V. Further, attention is also paid to a method of realizing a large area working of wire bonding, solder bump or the like by using a focused ion beam apparatus within a range of an acceleration voltage of about 3000 V in a large current region of constituting an amount of irradiating a focused ion beam to be equal to or higher than 1 nA.
Meanwhile, according to the charged particle beam apparatus, in order to carry out accurate observation or working, it is necessary to remove dimming referred to as off-axis aberration in accordance with adjusting a focal point position. An off-axis aberration is generated by a center of a charged particle beam that does not pass a center axis of an object lens, further specifically, caused by a deviation that is brought about between a center axis of an aperture of narrowing a charged particle beam to be incident on an object lens and a center axis of the object lens. Therefore, in order to carry out accurate observation or working by removing an off-axis aberration, it is necessary to adjust a position of the center axis of the aperture to coincide with the center axis of the object lens before being used.
In a background art, such an off-axis aberration has been removed specifically by the following method. That is, a center axis of an aperture is made to be disposed at an arbitrary position, and an image in a state of over focal point and an image in a state of under focal point are alternately acquired by adjusting a focal point position of the object lens. In a state in which the center axis of the aperture and the center of the object lens do not substantially coincide with each other, a position of the image described in the state of the over focal point and a position of the image described in the state of under focal point differ from each other, and therefore, when the focal point position of the object lens is changed, the acquired image is much changed. Further, the center axis of the aperture and the center axis of the object lens are made to coincide with each other by making the position of the image remain unchanged even when the focal point position is changed by repeating the above-described operation while adjusting the center axis of the aperture (refer to, for example, Nonpatent Reference 1).
Further, as another method, respectively in a state of over focal point and a state of under focal point, a charged particle beam is scanned on a knife edge, and an error of a current value detected by the knife edge by the state of over focal point and the state of under focal point is calculated. Further, a method of repeatedly changing to adjust a position of an aperture until the error of the current value falls in a predetermined range has been proposed (refer to, for example, Patent Reference 1). Nonpatent Reference 1: “Basic and Application of Scanning Electron Microscope”, Kyoritsu Shuppan K.K. Oct. 25, 1991, p.78-79
Patent Reference 1: JP-A-2005-276639
Problems that the Invention is to Solve
However, in the method according to Nonpatent Reference 1, a deviation of the center axis of the aperture is grasped only qualitatively from a change between the image in the over focal point state and the image in the under focal point state, and therefore, the adjustment of the center axis of the aperture can be realized by repeatedly carrying out the adjustment by manual operation based on the above-described phenomenon and an empirical rule. Therefore, in adjusting the center axis of the aperture, there poses a problem that technique of an operator and enormous time are needed. Particularly, when used in a large current region as described above, a working speed is fast, and therefore, a method of carrying out an adjusting operation swiftly to minimize damage of the sample is desired. Further, an adjusting accuracy is dispersed among respective operators, further, even when adjusted by the same operator, it is difficult to unify the adjusting accuracy among different apparatus, and a problem of bringing about a dispersion in a performance among apparatus is posed. Further, when the charged particle beam is irradiated in a low acceleration region as described above, the aberration of the charged particle beam is enlarged and dimming is brought about also owing to the fact that the acceleration voltage is a low voltage. Therefore, an aberration caused by the deviation of the center axis of the aperture and an aberration caused by the acceleration voltage cannot be separated from each other, and a problem that the center axis of the aperture cannot accurately be adjusted is posed.
Further, although in the method according to Patent Reference 1, the deviation of the aperture can be evaluated and adjusted quantitatively to some degree by the error of the current value and a correlative relationship between the error of the current value and the deviation of the aperture is not clear, and the deviation needs to be adjusted by repeatedly carrying out the adjusting operation. Therefore, similar to Nonpatent Reference 1, a problem of needing enormous time in adjustment is posed.
The invention has been carried out in view of the above-described situation and provides a charged particle beam apparatus and a method of adjusting an axis of an aperture capable of adjusting a position of a center axis of an aperture in a short period of time, easily and accurately.
Means for Solving the Problems
In order to resolve the above-described problem, the invention proposes the following means.
A charged particle beam apparatus of the invention is characterized by including a charged particle source of emitting a charged particle beam, an aperture for narrowing the charged particle beam to a predetermined diameter, an object lens for focusing the charged particle beam narrowed by the aperture to irradiate to a sample, observing means capable of acquiring an image of a surface of the sample, an aperture driving portion capable of moving a center axis of the aperture in an X direction and a Y direction constituting two axes substantially orthogonal to each other relative to the center axis, and a control portion capable of adjusting a position of the center axis of the aperture relative to a center axis of the object lens by moving the aperture by the aperture driving portion, wherein the control portion includes spot pattern forming means of forming a plurality of spot patterns on the surface of the sample by irradiating the charged particle beam to the sample by a plurality of times by moving the aperture to a position different in the X direction and the Y direction by the aperture driving portion, analyzing means for calculating positions of spot centers constituting centers of the respective spot patterns formed at the sample and a geometrical center position of a halo constituting an outer edge thereof from the image acquired by the observing means, and adjusting position determining means for calculating an adjusting position of the center axis of the aperture based on a position of intersecting lines of connecting the positions of the spot centers of the respective spot patterns and the center position of the halo calculated by the analyzing means, and wherein a position of the aperture is adjusted by moving the center axis of the aperture to the adjusting position calculated by the adjusting position determining means.
Further, the invention is directed to a method of adjusting an axis of an aperture of adjusting a position of a center axis of an aperture relative to a center axis of an object lens with regard to a charged particle beam apparatus for narrowing a charged particle beam emitted from a charged particle source to a predetermined diameter by the aperture and focusing the charged particle beam by the object lens to be irradiated to a sample, the method is characterized by including a spot pattern forming step of forming a plurality of spot patterns on a surface of the sample by making the position of the center axis of the aperture differ in an X direction and a Y direction constituting to two axes substantially orthogonal to the center axis and irradiating the charged particle beam to the previously prepared sample by a plurality of times, a spot analyzing step of calculating positions of spot centers constituting centers of the respective spot patterns and a geometrical center position of a halo constituting an outer edge thereof, an adjusting position determining step of calculating an adjusting position of the center axis of the aperture based on positions of intersecting lines connecting the center positions of the halos of the respective spot patterns and the position of the spot center, and a center axis position adjusting step of moving the center axis of the aperture to the calculated adjusting position.
According to the charged particle beam apparatus and the method of adjusting the axis of the aperture according to the invention, as the spot pattern forming step, the plurality of spot patterns are formed on the surface of the sample. That is, the spot pattern forming means of the control portion irradiates the charged particle beam to an arbitrary position of the surface of the sample by emitting the charged particle beam from the charged particle source. Thereby, at the arbitrary position of the surface of the sample, the spot pattern of a predetermined size is formed in accordance with a focal point state of the irradiated charged particle beam. Next, the spot pattern forming means of the control portion forms the spot pattern by moving the center axis of the aperture in the X direction and the Y direction by the predetermined moving amounts by the aperture driving portion and irradiating again the charged particle beam. Each of the plurality of spot patterns formed in this way shows a shape having the spot center constituting the center and the halo constituting the outer edge. The halo shows a range of irradiating the charged particle beam on the surface of the sample. Further, when the center axis of the aperture is positionally shifted relative to the center axis of the object lens, the spot center is formed at a position eccentric in the direction in correspondence with the direction of the positional shift of the center axis of the aperture relative to the geometrical center position of the halo.
Next, as the spot pattern analyzing step, the formed spot pattern is analyzed. That is, the analyzing means of the control portion calculates the positions of the spot centers of the respective spot patterns and the position of the geometrical center of the halo described in the image of the surface of the sample acquired by the observing means. Next, as the adjusting position determining step, the adjusting position of the center axis of the aperture at which the center axis of the aperture and the center axis of the object lens substantially coincides with each other is determined. That is, the adjusting position determining means of the control portion calculates the position of intersecting the lines of connecting the positions of the spot centers of the respective spot patterns and the center position of the halo as the adjusting position from a result of the spot pattern analyzing step. Finally, as the center axis position adjusting step, the control portion can bring about the state in which the center axis of the aperture substantially coincide with center axis of the object lens by moving the center axis of the aperture to the calculated adjusting position by the aperture driving portion.
Further, it is made to be further preferable that the above-described charged particle beam apparatus further includes scanning means capable of moving a position of irradiating the charged particle beam relative to the sample, wherein the spot pattern forming means of the control portion moves the position of irradiating the charged particle beam relative to the sample by the scanning means by amounts of amounts of moving the aperture respectively in the X direction and the Y direction multiplied by a constant value at every time of irradiating the charged particle beam to the sample by moving the center axis of the aperture.
Further, it is made to further preferable in the above-described method of adjusting the axis of the aperture that at the spot pattern forming step, a position of irradiating the charged particle beam is moved relative to the sample by amounts of respective moving amounts in the X direction and the Y direction of the aperture multiplied by a constant value at every time of irradiating the charged particle beam to the sample by moving the center axis of the aperture.
According to the charged particle beam apparatus and the method of adjusting the axis of the aperture according to the invention, when the plurality of spot patterns are formed at the spot pattern forming step, the center axis of the aperture is made to be disposed at the position which differs in the X direction and the Y direction, and the position of irradiating the charged particle beam is moved relative to the sample by the scanning means. Therefore, the plurality of spot patterns can be formed not to overlap each other on the surface of the sample, the image capable of further clearly identifying the spot pattern can be acquired, and the axis can be adjusted further accurately. At this occasion, by constituting the relative moving amount of the position of irradiating the charged particle beam by the amounts of the amounts of moving the center axis of the aperture in the X direction and the Y direction multiplied by the constant value, the moving direction can be made to coincide with the direction of positionally shifting the center axis of the aperture relative to the center axis of the object lens. Therefore, even when the position of irradiating is relatively moved as described above, at a search position determining step, the search position can be determined similarly based on the position of intersecting the lines of connecting the positions of the spot centers and the center position of the halo.
Further, it is made to be further preferable in the above-described charged particle beam apparatus that the control portion sets the charged particle beam to the sample in a state of an over focal point when the charged particle beam is irradiated to the sample by the spot pattern forming means.
Further, it is made to be further preferable in the above-described method of adjusting the axis of the aperture that at the spot pattern forming step the charged particle beam focused by the object lens is irradiated to the sample in a state of an over focal point.
According to the charged particle beam apparatus and the method of adjusting the axis of the aperture according to the invention, at the spot pattern forming step, by setting the charged particle beam in the state of the over focal point by the spot pattern forming means of the control portion to irradiate to the sample, in comparison with a state of an under focal point, the formed spot pattern can be formed to be larger. Therefore, at the spot pattern analyzing step, the spot pattern can further clearly be identified from the acquired image and a further accurate axis adjustment can be carried out.
Further, it is made to be further preferable in the above-described charged particle beam apparatus that the analyzing means of the control portion constitutes a binarized data constituted by processing to binarize the image acquired from the observing means and calculates the center position of the halo and the position of the spot center of the spot pattern based on the binarized data.
Further, it is made to be further preferable in the above-described method of adjusting the axis of the aperture that at the spot pattern analyzing step, a binarized data of processing to binarize the image of the surface of the sample formed with the spot pattern is formed, and the center positions of the halos of the respective spot patterns and the position of the spot center are calculated from the binarized data.
According to the charged particle beam apparatus and the method of adjusting the axis of the aperture according to the invention, at the spot pattern analyzing step, by constituting the binarized data of processing to binarize the image by the analyzing means of the control portion, the spot pattern displayed on the image can further clearly be identified and the further accurate axis adjustment can be carried out.